Opposite impacts of chemical oxidation for ofloxacin adsorption on activated carbon and carbon nanotubes

Exploration of the adsorption and desorption performance of volatile organic compounds by activated carbon with different shapes based on fixed-bed experiments

Activated carbon (AC) has been widely used in volatile organic compounds (VOCs) treatment of industrial exhaust gases. Rather than modifying specific pore size distributions and surface properties, altering the shape of AC offers a more feasible approach to enhance its adsorption performance. This study investigates the adsorption-desorption performance of two different shaped ACs with highly similar properties for the removal of VOCs. The clover-shaped AC (CSAC) has a 27.46% lower internal void fraction and a 39.10% higher external void fraction compared to cylindrical AC (CAC), resulting in denser packing and longer contact time with VOCs. Adsorption experiments showed the CSAC has 40% longer adsorption breakthrough (BT) times for ethanol, ethyl acetate, and n-hexane on average, and 20% higher saturation adsorption capacity per unit volume. CSAC also has higher partition coefficients, with the highest values for ethanol, ethyl acetate, and n-hexane being 0.0187, 0.0382, and 0.0527 mol kg-1·Pa-1, respectively. The desorption process for selected VOCs is non-spontaneous and endothermic. Optimal desorption conditions were identified as an inlet space velocity of 3535 h-1, a desorption temperature of 150 °C, and a pulsed inlet method. To investigate the possibility of the application of CSAC in real-world scenarios, xylene was chosen as a representative industrial VOC. Results showed CSAC has 20% higher BT time and saturation adsorption capacity for xylene compared to CAC under different bed heights. The desorption efficiency for xylene on both ACs is below 40%. With increasing xylene inlet concentration, the mass transfer zone (MTZ) height initially increases but stabilizes beyond 1704 mg m-3. At identical bed heights, the MTZ height of CSAC is 29% shorter than CAC, indicating a higher bed utilization efficiency.

Molybdenum disulfide nanoflowers - doped sodium alginate/polyvinyl alcohol porous xerogel for methylene blue and copper ion adsorption

In order to improve the adsorption performance of MoS2, as well as to solve the problems of MoS2-powder in adsorption, which is prone to agglomeration and difficulty to be recycled, we prepared MoS2-nanoflowers(MoS2-NFs), and mixed them with sodium alginate/polyvinyl alcohol(SA/PVA) to prepare MoS2-NFs/SA/PVA xerogel(MSP) by freezing-lyophilization. Then two forms of xerogels - block-MSP(MSPB) and spherical-MSP(MSPS) were prepared, and they were used as methylene blue(MB) and Cu2+ adsorbent. It was found that MoS2-NFs were evenly dispersed inside the SA/PVA with no agglomeration, while the interior of MSPB/MSPS showed the structure of parallel-pores and radial-pores, respectively. The adsorption capacity of MSPB/MSPS on MB can reach 233 mg/g, which is five times higher than SA/PVA-gel, showing excellent synergistic-adsorption effect, and the adsorption capacity for Cu2+ reaches 271 mg/g. The adsorption mechanism indicated that the adsorption of MB by MSPB/MSPS conformed to pseudo-first-order model, with electrostatic force as the main force. And their adsorption of Cu2+ conformed to pseudo-second-order model and was dominated by Lewis acid/base soft-soft interactions. Notably, after long-term adsorption, MSPB/MSPS maintains its shape and more than 90 % of the adsorption capacity, ensuring the recovery and reuse of materials. So, MSPB/MSPS has great potential in adsorption, providing a new solution for sewage purification.

Adsorption kinetics of ciprofloxacin and ofloxacin by green-modified carbon nanotubes

This paper investigated the uptake of CIP and OFL in single and multicomponent adsorptive systems using modified carbon nanotubes (CNTs) as adsorbent material. The characterization analyses of the pre- and post-process material by XPS, TG/DTG, FT-IR, SEM/EDS, and XRD helped in the elucidation of the mechanisms, indicating greater involvement of n-n and π -π interactions. In the kinetic studies, the simple systems with CIP and OFL were similar, both showed equilibrium time around 20/30 min and increased adsorptive capacity with increasing initial drug concentration. In the multicomponent system, different fractions of CIP and OFL were tested and the time to reach equilibrium also varied between 20 and 30 min. In general, the adsorption capacity of CIP is slightly lower than that of OFL under the conditions tested. The selectivity analysis of the system showed that the selectivity's of the two drugs are identical in equimolar fractions. The mathematical modeling of the kinetic data indicated that in monocomponent systems, the model of pseudo-second order (PSO) adequately described both CIP and OFL kinetics. Furthermore, with the implementation of Artificial Neural Networks (ANN), it was possible to obtain a more assertive prediction of the behavior of single and binary systems.

Highly Effective Removal of Ofloxacin from Water with Copper-Doped ZIF-8

Residual antibiotics in wastewater have gained widespread attention because of their toxicity to humans and the environment. In this work, Cu-doped ZIF-8s (Cu-ZIF-8s) were successfully synthesized by the impregnation of Cu²⁺ in ZIF-8 and applied in the removal of ofloxacin (OFX) from water. Remarkably, excellent adsorption performance was obtained in Cu-ZIF-8s, especially for Cu-ZIF-8-1, in which the adsorption capacity (599.96 mg·g⁻¹) was 4.2 times higher than that of ZIF-8 and superior to various adsorbents reported previously. The adsorption kinetics and adsorption isotherm follow the pseudo-second-order model and the Langmuir model, respectively. Furthermore, the removal efficiencies of OFX in Cu-ZIF-8-1 reached over 90% at low concentrations. It was revealed that electrostatic interaction and complexation play important roles in the adsorption process. In addition, the material can be regenerated by simple methods. Therefore, the obtained Cu-doped MOFs may have a promising application in the treatment of antibiotic-containing wastewater.

Combined Layer-by-Layer/Hydrothermal Synthesis of Fe3O4@MIL-100(Fe) for Ofloxacin Adsorption from Environmental Waters

A simple not solvent and time consuming Fe₃O₄@MIL-100(Fe), synthesized in the presence of a small amount of magnetite (Fe₃O₄) nanoparticles (27.3 wt%), is here presented and discussed. Layer-by-layer alone (20 shell), and combined layer-by-layer (5 shell)/reflux or /hydrothermal synthetic procedures were compared. The last approach (Fe₃O₄@MIL-100_H sample) is suitable (i) to obtain rounded-shaped nanoparticles (200–400 nm diameter) of magnetite core and MIL-100(Fe) shell; (ii) to reduce the solvent and time consumption (the layer-by-layer procedure is applied only 5 times); (iii) to give the highest MIL-100(Fe) amount in the composite (72.7 vs. 18.5 wt% in the layer-by-layer alone); (iv) to obtain a high surface area of 3546 m² g⁻¹. The MIL-100(Fe) sample was also synthesized and both materials were tested for the absorption of Ofloxacin antibiotic (OFL). Langmuir model well describes OFL adsorption on Fe₃O₄@MIL-100_H, indicating an even higher adsorption capacity (218 ± 7 mg g⁻¹) with respect to MIL-100 (123 ± 5 mg g⁻¹). Chemisorption regulates the kinetic process on both the composite materials. Fe₃O₄@MIL-100_H performance was then verified for OFL removal at µg per liter in tap and river waters, and compared with MIL-100. Its relevant and higher adsorption efficiency and the magnetic behavior make it an excellent candidate for environmental depollution.

Utilization of Ag2O-Al2O3-ZrO2 decorated onto rGO as adsorbent for the removal of Congo red from aqueous solution

The water resources contamination in an alarming concern for sustainable environment. This has led to development of new technologies and materials for waste water detoxification. In the present study, we have fabricated novel trimetallic based mixed oxides decorated reduced graphene oxide (rGO) composite using facile microwave method and utilized it as an adsorbent for the removal of congo red dye from aqueous solution. The final composite showed highly agglomerated metal oxides present on the rGO surface. The high surface area and activity of the synthesized adsorbent resulted in its high adsorption capacity of 333.32 mg/g for congo red. The Langmuir model better explained the isotherm data indicating the monolayer adsorption of congo red molecules onto Ag₂O-Al₂O₃-ZrO₂/rGO surface. The grander adsorption ability of Ag₂O-Al₂O₃-ZrO₂/rGO towards organic dye indicate its probable utilization in the removal of other dyes also from wastewater.